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Ovary, reproduction, and productivity of female columbian black-tailed deer Thomas, Donald Charles


Ovarian changes, patterns of reproduction, and age-specific productivity of female Columbian black-tailed deer (Odocoileus hemionus columbianus) on Vancouver Island were elucidated largely by examination of serial, stained sections of ovaries from 444 females. Well-defined, 8 or 9-day, follicular cycles occur during the breeding season in November and early December. Many follicles rupturing at first ovulation are asynchronous and of extreme sizes. Relatively small (4-5 mm³), short-lived (8-day) corpora lutea develop after first ovulation; these rapidly regress after second ovulation, while the corpora lutea of pregnancy grow to 100 mm³, within 5-8 days. The changes in ovarian structures during the breeding season were ascertained in 12 females, whose follicles and corpora lutea were dated by the cleavage stage of fertilized ova. These provided criteria for estimating ovulation dates in other females. In each cycle, about 50% of the adult females ovulated within an 8-day period. The mean date of first ovulation in each of the 5 years was approximately November 16; the second ovulation followed after a remarkably short period of 8-9 days. About 96% of the females conceived at second ovulation and 4% on subsequent ovulations. A high proportion of 'silent heats' accompany first ovulation, as indicated by lack of sperm on four of six ova. Growth curves, based on fetuses conceived at second ovulation, provided the conception dates of two late conceivers—those containing more than one generation of regressed corpora lutea of non-pregnancy. Females may cycle at least five times if pregnancy does not occur. Accessory corpora lutea develop in large and small unruptured follicles, in small ruptured follicles, and in regressing corpora lutea. They occurred in 47% of females between first and second ovulation and in 36% of pregnant females. Minimum loss of ova was 8.3% in all females that produced corpora lutea and 4.3% in females that became pregnant, of which 3.1% was moribund fetuses. Corpora lutea of pregnancy, corresponding to the number of fetuses, develop into distinctive scars, which persist for the life of the doe. Pregnancy rates of the previous season, as well as the long term productivity of individuals and the population, were estimated from these. The average number of viable fetuses per doe increased progressively from 0.91 in yearlings to 1.81 in the 5-5 to 6.5 age-classes, and thereafter decreased. These changes in fertility with age were mirrored by changes in weight and girth. The relative contribution of fawns by each age-class in the population progressively decreased with age. One hundred females of reproductive age produced about 137 fawns.

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